This invention relates to dental posts, and more particularly to a dental post with an active upper portion and a passive lower portion, which improves its retention within a prepared tooth stub on which a dental restoration will be erected. In addition, this invention relates to the use of a sleeve with an active portion positioned in a tooth stub. The active portion of the dental post is engaged with the active portion of the sleeve to improve its retention within the prepared tooth stub. Furthermore, this invention contemplates forming the sleeve by positioning a mandrel with an active upper portion in an adhesive prepared bore in a tooth stub and curing the adhesive to form the sleeve. In one embodiment the adhesive is cured by transmitting light through the mandrel to cure the adhesive.
In restoring dentition, one procedure is to build up a dental prosthetic structure on a tooth stub. The tooth stub is initially prepared by cutting it down to provide a suitable support on which the prosthetic structure will be built. A bore is formed into the tooth stub in which a dental post is inserted. In one type of dental post, referred to as an active post, there are threads provided on the post and the post is threaded into the bore in the tooth stub. Other posts are referred to as passive posts and they are secured in the bore by means of cement. The passive posts typically include a contoured surface for improving its retention in the bore formed in the tooth stub. Suitable dental cement is used for retaining the dental post in the bore. A portion of the dental post extends upwardly above the surface of the tooth stub so that as the dental prosthetic structure is formed or built up onto the tooth stub, it is retained in place on the tooth stub by means of the extending portion of the dental post.
By way of example, an early type of active post has been suggested in U.S. Pat. No. 702,111 describing a post with screw threads which are screwed into the root cavity of a tooth. Threaded engagement of an active post into the dentin of a tooth has been found to cause stress in the tooth thereby contributing to its possible fracture. On the other hand, using passive posts produce less stress in the tooth. However, the retention of passive posts are not as great as the active post. To improve the retention, various types of contoured surfaces have been suggested. By way of example, U.S. Pat. No. 4,479,783, issued Oct. 30, 1984 for "Helically Fluted Dental Post", assigned to the assignee of the present invention, suggests contouring the surface of a passive dental post with helical flutes in a sequence with designated flutes being deeper than alternating shallow flutes to improve retention of the dental post. Improvements in the capabilities of dental posts are also described in U.S. Pat. No. 4,729,736, issued Mar. 8, 1988 for "Contoured Dental Posts", assigned to the assignee of the present invention, which includes helical grooves and annular retaining ledges axially spaced along the post to both improve retention of the post and increase the strength of the post to reduce the possibility of post shear.
The us of sleeves in a prepared bore of a tooth stub has been suggested in the prior art related to retention of a dental post within a bore in a tooth stub. By way of example, there has been suggested in U.S. Pat. No. 965,246 the use of a sleeve in a cavity in a tooth stub into which a pin attached to a crown is inserted and held either by friction or cement. In addition, U.S. Pat. No. 4,622,012 suggests the use of a sleeve positioned in a bore of a tooth through which an adhesive is introduced into the bore. A dental post is then introduced into the sleeve to force the adhesive through holes in the sleeve to distribute the adhesive in the bore. Upon hardening of the adhesive, the post is retained in the sleeve.
While the aforementioned dental posts and sleeves have provided improvements with respect to the retention of a post in a bore, still further improvements in such retention would be beneficial. These improvements would be particularly beneficial if they can be achieved without increasing the risk of breaking the dental post or adding stress to the tooth.